The term "crypto-marking" is used in the present specification to designate marking which is concealed and invisible in a hidden location on the object, known only to its proprietor and undetectable by third parties.
The invention is particularly applicable to identifying works of art such as: paintings, sculptures, ceramics, pottery, vases, furniture, ancient clothes, carpets, tapestries, ancient books, engravings, etchings, collectors' items, etc.
The invention is also applicable to identifying modern durables such as cars, stereo systems, computers, televisions, radios, video recorders, cameras, etc.
The invention is also applicable to providing protection for all sorts of documents and official papers against forging, and in particular bank documents, checks, contracts, wills, paper money, identity documents, legal papers, etc.
At present there are very few means for protecting valuable objects such as works of art or other movable property against theft, resale, or forging. In addition, it is very difficult for an owner to be able to provide irrefutable proof of ownership of an item of stolen or resold property, once it has been found.
Another difficulty stems from the fact that not all works of art are listed. Although paintings by great masters may indeed be listed, the same does not apply to furniture, in particular.
According to folk wisdom: "possession is nine-tenths of the law". In France, this concept is laid down more formally in Article 2279 of the Civil Code which states:
"For movable property, possession gives title. Never-the-less, anyone who has lost a thing or an object, or from whom it has been stolen may, during a period of three years counted from the day of loss or theft, claim back that thing or object from any person in whose hands it is found; without prejudice to any remedy which that person may have against a third party from whom he obtained the thing or object."
Under these conditions, it is absolutely essential in the event of theft or loss to be able to prove ownership in goods, should the goods ever be found in the hands of a third party.
Presently existing means for protecting valuable objects, in particular works of art, include using metal implants which the owner of the object inserts in a special location on the object, known only to the owner.
Thus, in the event of loss or theft, if the object is found in the hands of a third party, the owner is theoretically in a position to prove ownership by taking out the implant or by causing the object to be X-rayed in the region containing the implant.
Unfortunately, a procedure of this type is not completely reliable since the implant may be detected by the third party, e.g. by using X-rays or gamma rays.
Proposals have also been made to apply a selective chemical compound or "target" compound on the object to be protected, which compound is suitable for subsequent detection by any appropriate means, in particular by means of another chemical compound or "probe" compound.
Thus, European patent application No. 0 090 130 proposes a method of authenticating a document by means of a color reaction system using a color-forming substance and a color-developing substance. One of the two substances is applied to the object, while the other substance is used for detection purposes. When the two substances are put into contact with each other, a characteristic color-reaction takes place, thereby enabling the document to be authenticated.
Given the limited number of color reaction systems suitable for this application, such a method is also lacking in reliability.
Consequently, an object of the invention is to provide a method capable of giving irrefutable proof of ownership of a valuable object, in particular of a work of art.
Another object of the invention is to provide a crypto-marking method capable of guaranteeing that a valuable object can be identified, with the marking itself being suitable for being delivered and performed by a valuer using the method of the invention.
Another object of the invention is to provide a method suitable for identifying official documents and papers such as contracts, deeds, wills, official papers, folding money, checks, share certificates, etc.
Another object of the invention is to provide such a crypto-marking method in which the marking of the valuable object cannot be detected by a third party, in particular by detection methods based on X-rays or on gamma rays.
Finally, another object of the invention is to provide a crypto-marking apparatus suitable for implementing the method of the invention.
The invention provides crypto-marking of valuable objects by taking advantage of the spectacular progress that has been made in biology over the last few years, making available molecular tools which are very highly effective. Of the various advances that have been made, the nucleic probe technique certainly constitutes the tool which is the most attractive and the most powerful.
The nucleic probe technique is based on the high degree of affinity which exists between two complementary strands of nucleic acid. This affinity is well illustrated by theoretical estimates of the dissociation constant Kd for a hybrid or "duplex" of 273 base pairs.
This value is about 10.sup.-23 M at 5.degree. C. below the half denaturation temperature (Tm) of the duplex. By way of comparison, antigen-antibody actions have a Kd in the range 10.sup.-5 M to 10.sup.-9 M.
Using this technology, it is possible to construct nucleic probes (probe nucleic acids) of sequences that are complementary to the sequences of target nucleic acids and to perform duplex formation in vitro.
If the probe is labelled, radioactively or otherwise, the duplex formed in this way can be detected.
The use of nucleic probes thus makes it possible to detect living organisms (all of which normally carry nucleic acids representative of their genetic inheritance), providing the sequence or a portion of the sequence of the nucleic acids of said organisms is known.
The previously labelled probe is suitable for hybridizing with the target nucleic acid contained in the organism under consideration causes a hybrid or duplex to be obtained, and the labelling makes it detectable.
Numerous viruses, bacteria, parasites, fungi, etc. can thus be detected in biological media.
Nucleic probes also make it possible to perform genetic studies on more complex living organisms such as plants, animals, and human beings.
Such studies can be used, for example, to investigate and avoid genetic disorders, to identify the father or the mother in an affiliation action, to identify a rapist or a criminal amongst suspects, etc.
So far, nucleic probes have been used solely in medical, agro-food, or scientific applications for which nucleic acids and in particular nucleic probes constitute a powerful tool.
Surprisingly, the Applicant has observed that nucleic probe technology may also be used successfully in protecting valuable objects, in particular works of art, by providing absolutely irrefutable proof of the ownership of objects that have been stolen, resold, or forged, providing only that the objects were previously marked by the method of the invention.